Oil flow control



The present invention relates to control of fluid flow into wells, and particularly pertains to such fluid flow through wells drilled into a loose or incompetent formation. In one of its more specific embodiments this invention is directed to a method of controlling or even preventing inflow of sand or of other earth particles into wells producing oil, gas and/ or water from loose formations. The present invention may also be stated to be directed to a method of inhibiting or totally preventing the earth particles from incompetent formations penetrated by a well-bore from being carried into the well-bore by fluid, e.g. petroleum, produced from or through this earth formation.

The usual difficulty of obtaining a fluid from an incompetent formation through a well drilled thereinto is that earth particles, eg. sand particles, are carried into the well with the fluid. This frequently leads to collapsing or sloughing of the well-bore walls. When such condition exists, the walls of the well-bores must be supported, eg. by a pipe, which may be a well casing or liner, provided with perforations or other types of openings, where said pipe penetrates the producing strata, said perforations or openings comprising round holes, oblong holes, rectangular slots,-or the like, or the pipe may be in the form of a tubular screen, to permit the inflow of fluids therethrough and into the wells, These perforations, however, frequently allow considerable quantities of earth particles, e.g. sand, entrained in the fluid to be carried into the well. The relatively smaller or finer particles of the sand thus entrained usually remain suspended in the flowing fluid, and are produced at the wellhead together with the rising fluid. This causes abrasion of metal parts in the producing wells and lines, and also necessitates frequent cleaning of production service equipment, e.g. oil-gas separators, tanks, etc. The coarser particles entrained by the fluid flowing from the information into the wells through the perforations in the casing or liner are not usually carried upwardly to the well head, but normally drop out and are deposited in the bottom portion of the casing or liner. This sand accumulation in the bottom of a well will gradually reduce the rate of production of the well because the perforations in the casing or liner opposite the producing portion of the formation will become successively covered by the gradually increasing mass of sand and'other relatively coarse earth particles which thus settle in the interior of the perforated casing or liner. In fact, the production of such a well may cease completely when the settled particles cover the space in the cased well up to the uppermost perforations. At this stage, the well has to be taken off production,

and has to be cleaned out to the bottom of the perforated casing of liner before a new production cycle can be initiated. Obviously, this type of operation is costly and uneconomical both due to the high cost of cleaning and the loss of production during the gradual sanding and the time during which the Well is being cleaned and placed States Patent ice and to provide a method whereby fluid flow of wells of v the above-mentioned type (namely, those drilled into loose or incompetent formations and provided with perforated pipe therein) may be controlled in such a manner that the earth particles of such incompetent formations are prevented or at least materially inhibited from entering (through the casing or liner perforations) into the well-bore.

It is another object of the above invention to provide a method whereby wells drilled into incompetent or loose formations, which wells are provided with a casing, liner or like pipe set therein and having perforations opposite such incompetent formations, may be controlled so that flow of fluid thereinto from said loose or incompetent formations may be carried out while preventing, or at least materially inhibiting the inflow thereinto of particles of the loose formations. A still further object of the invention is to clean such treated wells, without the necessity of pulling the pipe (e casing), when the annular space surrounding the perforated portion of the pipe becomes so clogged with the aforesaid earth particles that back on roduction; Insothe cases, the large amounts of sand and the like" enteringand depositingin the encased well make such cleaning uneconomical, which frequently necessitates the abandonment of the well.

It is one of the main objects of the present invention to obviate the above and other defects of the prior art,

flow of fluid therethrou'gh and into the well materially decreases or even ce'ases' completely. 7

The above and other objects of the invention may be attained or realized by supply pieces or chunks of permeable elastic material (e.g. chunks of foams of elastomeric materials) to the bottom of a wellbore provided with perforations adjacent the incompetent formation,- this introduction of the elastic material being normally effected by means of a carrier fluid through the pipe or conduit provided in the well, forcing said carrier fluid together with said pieces of permeable elastic material through the perforations into the space outside the perforated pipe, thereby filling at least part of the surrounding space adjacent to said loose or incompetent formation, terminating the injection of the carrier fluid, and reversing the flow through the pipe perforations to cause fluid in the incompetent formation to flow to and into the well-bore. Under these conditions the pieces of permeable elastic material present in the space surrounding the perforated pipe will then be caused to be moved by the fluid produced by the formation towards said perforations, these permeable elastic pieces covering said perforations in such manner that the fluid produced can pass therethrough (due to the permeable nature of the elastic material) while the passage of the earth particles, e.g.- sand, is prevented or at least materially inhibited.

More particularly stated the invention comprises a method of inhibiting the flow of earth particles from incompetent or loose formations into well-bores drilled into such formations, which well-bores are provided with a suitable pipe, e.g. casing or liner, having perforations opposite' or near said incompetent formations, this method comprising suspending pieces of a permeable elastic material (cg. a foam of an elastomeric material) in a Suitable carrier fluid, these elastic pieces being (at least during a part of the operations of the method) larger in size than said pipe perforations, conveying the suspension thus formed down the well, forcing the carrier fluid together with the pieces of elastic material through the perforations and into the space outside said perforated pipe (thereby filling at least partially the space between said perforated casing and the contiguous incompetent formation), terminating the injection of the carrier fluid, and reversing the flow through the pipe perforations to cause fluid in the incompetent formation to flow into the wellbore.

Other features, facets and modifications of the process of the present invention will be apparent from the following description.

As indicated above the pieces of elastic material are preferably so chosen that they are larger in size and cross-section than the perforations through which they are to be forced into the formation. Since these pieces are of an elastic nature (elastomers), they can be forced through said perforations. However, the return of these pieces from the outside of the perforated pipe into the interior of the well-bore can not occur because the pres sure differential existing across the perforations covered by these pieces during the production of the fluid from the formation into the well-bore is smaller than the pressure differential existing across said perforation during the injection of the carrier fluid laden with these pieces outwardly into the space surrounding the perforated pipe. Of course, if so desired one may first inject through the perforations elastic pieces having relatively smaller crosssection followed by those having a larger cross-section. In fact one may, if so desired, first introduce into the we1l and through the perforations into the formation elastlc pieces which are smaller in cross-section than the perforations, and then introduce elastic pieces having a size larger than the cross-section of the perforations so that these latter pieces, when the well is put on production will cover the perforations on the outside of the pipe and prevent inflow of earth particles while permitting inflow of fluid such as petroleum.

Any permeable elastic material (i.e. permeable elastomer) may be used in the process of the present invention. As indicated above the size of the pieces will depend on the type, nature and size of the perforations in the casing or liner disposed in the well-bore. As to the character of the elastic material, it may consist of any foam of an elastomeric material, e.g. a foam plastic, a foam rubber, or any other substance or material having a similar property, namely the property of being able to be compressed and pushed through the perforations and to expand thereafter; the pieces must have passages therethrough which will permit fluid flow therethrough, e.g. flow of oil, gas, water or the like, but will prevent or materially inhibit the flow therethrough of any earth particles suspended in said fluids. As such elastomeric foam (i.e. permeable elastic material) one may use a polyurethane foam plastic or foam rubber, which latter may be a hydrocarbon type or chloroprene type foam rubber. Of course, in order to be effective in the process of the present invention these materials should be in the form of a foam-type material so that fluid flow therethrough can be maintained when these foam-type elastic permeable materials have been forced through the perforations and thus disposed in the annular space around said perforations.

As the carrier fluid for the conveyance of the aforesaid permeable elastic foam-type material, one may use any suitable fluid which is non-reactive with the pieces of the elastic material. The fluid should not cause their disintegration or other undesirable changes therein. Also, this fluid should not have a detrimental effect on the subsequent production of the well. As a general rule it is preferable to use the same type of fluid as that which is being or to be produced from or through the incompetent formation into which the well-bore has been drilled. Thus, in oil-bearing formations it is preferable to use hydrocarbons, particularly crude oil, or fractions thereof. However, in some instances it may be possible or even desirable to use such materials as water as the carrier fluid.

It has been pointed out that one of the objects of the invention is to provide a method according to which the permeable elastic material (elastomeric foam) disposed in the annular space surrounding the perforated portion of the pipe may be removed in case this material has become plugged or otherwise worn out, said removal to be eifected without the necessity of physically pulling out the perforated pipe to thus permit the inflow of this deteriorated elastic material; Of course, one method of doing this would be to create or develop such a high pressure diflerential across the perforations that the pieces of elastic material will be squeezed and forced back into the well. However, such a technique is usually highly undesirable because of the tremendous stress placed on the incompetent formation with the resultant sloughing of the formations and possible complete clogging of the well which may necessitate abandonment thereof. According to one phase of the present invention this removal of the permeable elastic material from the space surrounding the perforated pipe is attained by introducing through the well-bore and into the space containing this permeable elastic material a material capable of disintegrating the permeable elastic pieces. This disintegrating agent is then allowed to remain in contact with the permeable elastic material for a sufficient period of time necessary for the disintegration to be carried out, after which the agent together with the disintegrated material may be pumped out or otherwise removed from the well, and a fresh batch of permeable elastic material may then be introduced into the well and through the perforations or openings in the pipe in the manner set forth above. This method may be particularly advantageously used in connection with wells completed under water because this manner of introducing and replacing the sand-screening permeable elastic material does not depend on the use of tools in the wellbore.

The nature and character of the disintegrating agent may vary within wide limits particularly depending on the type and character of the elastic material employed. Thus, for example, one may mention sulfuric acid and ethyl acetate for dissolving cellulose sponges, toluene for dispersing acetate sponges, acids such as sulfuric or hydrochloric acid, for dispersing polyurethane foam used for sand-screening processes, as well as aromatic solvents for the removal of foam rubber type sand-screening sponges.

The following illustrative example is presented to describe the manner in which the process of the present invention can be used. An oil well, which is completed with a perforated liner opposite a producing stratum, or in which part of the cemented casing string opposite a producing zone is gunperforated or otherwise perforated may have a part of the producing stratum directly surrounding the casing or liner consisting partly or wholly of poorly consolidated or unconsolidated sands. This part of the stratum will then be unable to stand up through lack of support in front of the perforations. As a result, these loose sands will tend to force themselves through the perforations into the interior of the casing or liner, this being aided by the fluid flow from the formation into the casing or liner via the sand perforations. Thus, sand voids or spaces free of sand are created in the space surrounding perforated sections of the pipe, i.e. perforated casing or liner.

For filling up these spaces with a permeable elastomeric material for sand-screening purposes, a fluid (preferably oil) carrying permeable elastic pieces in suspension is injected through the well-head into the well. In cases where the well is a single zone well, this mixture of carrier fluid and elastic pieces may be pumped directly down the tubing-casing annulus. For wells producing from multiple zones, it will be more effective to treat individual zones separately, e.g. by injecting the above suspension down through a tubing with a packer set above each interval, or to use a straddle-type perforation washer.

As stated, the sand-screening material, for which purpose one can use bodies or pieces manufactured of any permeable, elastic foam plastic, is added to the carrier fluid, transported to the bottom of the hole, and forced together with the carrier fluid through the perforations provided in the pipe. Also, as indicated, and ifdesired,

the pieces used can" at first be of a size which is relatively small with respect to the perforations they havet'o pass. This will permit the use of relatively low differential pressures to force them through the perforations. It will be obvious that a large portion of this material will passthrough perforations opposite the channels, fissures and other spaces in the strata having the lowest flow resistance. By progressively adding larger pieces (i.e. pieces having a cross-section larger than the perforations) to the carrier fluid, these perforations opposite low-resistance zones will be temporarily plugged, whilst the perforations having a high-resistance will start to take the larger pieces of the sand-screening. material. Finally, when all the perforations are plugged by the larger pieces, the injection rate of the oil is increased. Consequently, the pressure differential across the plugged perforations will also increase whereby the pieces will be forced through the perforations into the space or spaces surrounding the pipe; This passage is possible since the elasticity allows the pieces to be sufficiently deformed so as to pass through the perforations. When these pieces enter the sand voids or spaces surrounding the pipe, they will regain their former dimensions. After a suflicient quantity of material is injected, the operation is stopped, and the well is brought on production. The produced oil will flow out of the formation and through the perforations, in the meantime moving the pieces present on the outside of the perforated pipe towards perforations. The pieces will thus accumulate and cluster around and over the perforations in such a way that the oil has to pass through the permeable pieces but the sand is retained by them. The said particles which are not retained by the filter action of the permeable pieces are of such a small size that they are readily lifted by the oil flow to the Well-head, and do not settle out in the bottom of the well. Also, their amount and size are such that little or no erosion is caused by them.

Since the produced oil flows through the perforations at a rate which is less than the injection rate at which the sand-screening material has been forced through the perforations, the pieces having cross-section larger than the perforations will not return through the perforations. The pieces having cross-section smaller than the perforations also remain in the annular space surrounding the perforations, this because they are prevented from passing through the perforations by the later introduced larger pieces disposed on the surface of said perforations.

It is to be noted that the pieces will remain in the annular space surrounding the perforations even if the flow of oil is stopped: this is due to the packing action of the sand surrounding the liner or casing.

In one specific well, excessive trouble was encountered by unconsolidated sand passing through perforations shot through a casing by /2 bullets. Economic production of this well was impossible because in 2 /2 days only 10 barrels of oil were produced containing 36% sand.

After carrying out the method of the present invention as described above, the well was put back on production and produced a viscous oil at a rate of about 33 'bb1s./ day. No sand was produced.

The pieces of foam plastic used were at the beginning of the injection of small sizes (2. cm. x 3 cm. x 5 /2 cm. and 3 cm. x 4 cm. x 6 cm), and of larger size (3 cm. x 7 cm. X 8 cm.) at the end thereof. During the injection a steady rise in pressure was observed at the well-head from 500 to 1700 p.s.i. A series of pressure build-ups followed by sudden pressure-drops were observed indicating that the pieces were being forced against and then through the perforations. The build-ups were initially equal to about 50-100 p.s.i., but later on increased to 200 p.s.i. when the larger-sized pieces were being forced through the perforations.

When the permeable elastic material has to be removed in case it is worn out or plugged, this can be performed by removing liner and washing the well, after which the liner is replaced' and} afresh batch of permeable elastic material is p'r'irhp'ed dawn the Well! 7 In another, more simpleway, the permeable elastic ma-' terial' can be removed from the well by pumping a disintegrating a'gentdown the well. The permeable elastic material is thusdisintegr'at'ed, and can be removed from the bottom of the wellby pumping out the well. After cleaning the wellof the sand which mighthave entered the well, during this pumping action a fresh charge of permeable elastic material is pumped down the well in the manner as hereinbefore described.

The term pipe, as used herein and in the appended. claims, includes any casing or liner disposed in a wellbore ,to prevent the sides of said well-bore from collapsing.

The foregoing exemplary description of the invention is not to be considered as limiting since many modifications and variations may be made within the scope of the following claims by those skilled in the art without departing from the true spirit and scope thereof.

We claim as our invention:

1. The process of inhibiting the inflow of earth particles from incompetent formations into well-bores drilled into said formations, which well-bores are provided with a casing having perforations opposite said incompetent formations, which comprises suspending pieces of a permeable elastic material in a carrier fluid non-reactive therewith, said pieces being substantially larger in all directions than all of said casing perforations, conveying said suspension down the well-bore to substantially the bottom thereof, forcing said carrier fluid together with said elastic pieces through the perforations and into the space outside said casing, thereby to fill at least partially the space between said perforated casing and the contiguous incompetent formation, terminating the injection of the carrier fluid, and reversing the flow through the casing perforations to cause the fluid in the incompetent formation to flow into the well-bore.

2. The process according to claim 1, wherein, prior to the introduction of pieces of elastic material of a size larger in cross-section than the cross-section of the casing perforations, one introduces into the carrier fluid, and therefore through the well and into the annular space outside said casing pieces of elastic material which are of a smaller size.

3. The process according to claim 1, wherein the pieces of elastic material comprise pieces of a permeable foam plastic.

4. The process according to claim 1, wherein the pieces of elastic material comprise pieces of foam rubber.

5. The method of inhibiting inflow of earth particles from an oil-producing incompetent formation into a wellbore drilled thereinto, which well-bore is provided with a pipe having openings therein substantially opposite said incompetent formation, which comprises suspending pieces of a permeable elastomeric material in a hydrocarbon, said pieces being substantially larger in all directions than said pipe openings, introducing said suspension into the well-bore, forcing said suspension downwardly through said well-bore and the interior of said pipe and to and through the openings therein, continuing said passage of the suspension until substantially all of the pieces of, elastomeric material have been forced through said pipe openings and into the annular space surrounding said pipe, thereby filling at least partially the space between the pipe and the contiguous incompetent formation, terminating the injection of the hydrocarbon, and reversing the flow through the pipe openings to cause the oil from the incompetent formation to flow through the permeable elastomeric material into the interior of the piped well-bore.

6. The method of inhibiting inflow of sand particles from an oil-producing unconsolidated sand formation into a well-bore drilled thereinto, which well-bore is provided with a casing having perforations therein opposite said unconsolidated formation, which comprises forming a suspension of pieces of a permeable elastomeric material in a hydrocarbon, said pieces being larger in crosssection in all directions than all of the perforations in the casing, introducing said suspension into the cased well-bore forcing said suspension downwardly through the casing under a pressure sufiicient to force said suspension and therefore the elastomeric pieces through the casing perforation, continuing said passage of the sus pension until substantially all of the elastomeric pieces have been thus forced through the perforations and into the space surrounding said perforated casing, terminating the injection of the hydrocarbon, and reversing the flow through the perforated casing to cause the oil to flow into the well-bore.

7. The method according to claim 6, wherein the elastomeric material employed comprises a hydrocarbon rubber foam.

8. The method according to claim 6, wherein the elastomerie material employed comprises a chloroprene rubber foam.

9. The method according to claim 6, wherein the elastomeric material comprises a urethane foam plastic.

10. The method according to claim 6 wherein the flow of oil into the well is terminated when the elastomeric material surrounding the perforated casing becomes undesirably clogged, an agent capable of disintegrating said elastomer is introduced thereinto and maintained therein for a suflicient period of time to disintegrate the elastomer, after which said agent and the disintegrated elastomer are withdrawn from the well, and the process of claim 6 is repeated.

References Cited in the file of this patent UNITED STATES PATENTS 2,207,334 Reynolds et a1. July 9, 1940 2,356,769 Layne Aug. v29, 1944 2,699,212 Dismukes Jan. 11, 1956 2,775,303 Abendroth et a1. Dec. 25, 1956 

